PROJECT SUMMARY/ABSTRACT Kaposi's sarcoma associated herpesvirus is the etiological agent for several malignancies in the human population including Kaposi's sarcoma (KS), Multicentric Castleman's disease (MCD), and primary effusion lymphoma (PEL). Although innate immunity has been shown to be important for comprehensive antiviral responses to clear viral infection and limit viral tumor growth and proliferation, exactly how the innate immune system senses tumor viruses, such as KSHV, is not well understood at the molecular level. Investigating the interplay between the innate immune system, KSHV and KSHV-associated cancers will help us develop better therapies to not only treat KSHV related malignancies, but also broaden our knowledge to other viral cancers. Previously, we have found that cGAS-STING pathway is responsible for triggering innate immune responses upon KSHV infection. However, KSHV can still establish lifelong infection in the presence of cGAS-STING signaling, suggesting KSHV viral regulation of cGAS- STING pathway to suppress innate immunity. In order to identify potential viral regulators, we have developed a screening system and successfully identified multiple viral proteins that negatively regulate cGAS-STING signaling. We have also validated one of our candidates, vIRF1, and explored the mechanism of how vIRF1 blocks cGAS- STING pathway to facilitate KSHV replication. Our results suggest that modulation of cGAS-STING pathway is important for viral transmission and the lifelong persistence of gammaherpesviruses in the human population. Therefore, studies in this K99/R00 proposal will build upon these findings to extend our knowledge of how these viral proteins regulate cGAS-STING pathway and how to develop potential KSHV cancer therapy by targeting these viral proteins. Specifically, I will focus on: 1) Validating our screening results and exploring detailed mechanisms of cGAS-STING signaling regulation by our KSHV viral candidates, 2) Utilizing multiple technologies, including siRNA, recombinant virus, and CRISPR to explore the role of our viral candidates on KSHV pathogenesis in vitro, 3) Utilizing CRISPR technology to explore the role of our viral candidates in our PEL based mouse model, 4) Screening for drugs that target cGAS-STING pathway, and testing their efficacy in our PEL based mouse model. With strong mentorships and a detailed training plan, I aim to build a solid foundation for a successful independent research career investigating the interaction of cGAS-STING pathway and KSHV cancers and developing potential KSHV cancer treatments.